


The Fantastical Mysteries of Mermaid Reproduction

by 8ball



Series: Ocean's Child [3]
Category: One Piece
Genre: Established Relationship, Idiots in Love, M/M, mermaid au, mermaid sex and anatomy things, mermaid!Sanji, otherwise known as zoro figuring out how to have sex with his boyfriend, pre-drum, sorry no chopper yet
Language: English
Status: Completed
Published: 2020-06-04
Updated: 2020-06-04
Packaged: 2021-03-04 06:00:52
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 6,515
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/24538894
Author URL: https://archiveofourown.org/users/8ball/pseuds/8ball
Summary: How the fuck did mermaids have sex? Zoro hadn’t thought he'd ever be asking himself that question, and yet there he was. What if there were secret mermaid customs Zoro didn't know about? What if there was some kind of mating ritual? Would he have to dance? What if it took place underwater? How would he breathe? It was complete bullshit that all the books on mermaids were about claimed sightings and appearance and not even a little about their reproduction.He decided that he’d just have to take the risk and ask Sanji for the details. If he didn't get hit in the face with a tail for asking, then he’d move forward from there.
Relationships: Roronoa Zoro/Vinsmoke Sanji
Series: Ocean's Child [3]
Series URL: https://archiveofourown.org/series/1757041
Comments: 26
Kudos: 479





	The Fantastical Mysteries of Mermaid Reproduction

**Author's Note:**

> was gonna post this for the end of mermay whoops  
> anyways no excuse for this just wrote mermaid smut a while back and decided to finish it eyy

Zoro watched Sanji move around in his kitchen tank, leaning up and over the sides to reach one thing or another as he cooked. Water sloshed over the side of the glass to leak on the always-damp floor, and he muttered curses whenever he dropped a bit of spice or a slice of onion in the water. It was incredibly entertaining to watch. 

“And you’re not in human form for this because...why?”

Sanji gave him a flat look over his shiny shoulder. Zoro was always struck by how vivid his eyes were when he went full mermaid, the blue turning something almost metallic, if that was the right way to describe it. They just seemed to  _ glow _ . 

“If you always had to concentrate on making your lungs work properly while you went about your day you’d get tired of it too.”

Zoro’s brow furrowed in confusion. 

“If breathing is a pain in the ass while you’re human then why do you  _ smoke _ ?”

Sanji waved a spatula around dramatically, tail flicking more water on the floor. 

“Hey, if those lungs are gonna be a bitch to me then I’m gonna be a bitch to them.”

“Because taking petty revenge on an organ makes sense.”

“Your face doesn't make sense.”

“Says the cooking mermaid.”

Sanji splashed at him, and he didn't bother dodging. If Zoro had learned anything in the months of sailing with Sanji it was that spending time with him almost always resulted in getting wet. Just entering the galley alone was a hazard for anyone, especially Luffy. Nami had taken to using an umbrella when meals got rowdy.

Usopp stuck his head in the room, eyes immediately locking on to the tank. He had a little notebook in hand, which meant he’d probably come up with more mermaid-based inventions to dazzle the cook with. Sanji paused his cooking to glare at the sniper.

“If I have to say no to your fin-rollerskates one more damn time…”

Zoro stifled a laugh as Usopp waved his hands in a dismissive gesture.

“Nah, those were just a prototype anyways. I’ve come up with something  _ way  _ better!”

Usopp opened the notebook, puffing his chest out proudly. Zoro leaned in with Sanji to get a look. He raised a brow at the drawing, sharing a look with the cook before turning back to Usopp. 

“...a wheelchair?”

Usopp made an undignified noise, wrenching his notebook back.

“I’ll have you know it's the  _ Usopp-mermaid-mover-express _ and it took  _ hours _ of thought and consideration!”

Sanji leaned back into his tank, resting his chin on the edge lazily. 

“Ok then, what makes it  _ not _ a wheelchair?”

Usopp placed a hand on his chest like he’d been insulted beyond belief. He pointed dramatically to Sanji. 

“It's a  _ mermaid _ transporter! It's for  _ mermaids _ ! Note the height of the wheels, the breaks, the comfortable rest for the  _ tail _ ! Could a  _ human _ sit in that!?”

Sanji and Zoro looked at each other. 

“Yes?”

“Yeah?” 

Usopp flung his hands up in defeat, leaving the galley as he muttered to himself. The two men watched him leave before making eye contact. Sanji asked the obvious question first. 

“It  _ was _ a wheelchair, right?”

Zoro shrugged. It had sure as hell looked like a wheelchair. 

“I guess-

It hit them both at the same time just how  _ close  _ they were, causing a mutual embarrassed fumbling. Zoro looked away at the wall very quickly, cheeks burning. He could hear Sanji going back to cooking, movements overly loud and clumsy. Coughing awkwardly, Zoro immediately wished he had something to do with his hands too. That train of thought led him to just what exactly he  _ could _ do with his hands and Sanji and oh hey the wall has some dirt on it and isn't that just fascinating? 

Zoro crossed his arms very firmly and pointedly looked at the speck of dirt on the wall. This was not the first time he’d ended up in this situation, as embarrassing as that fact alone was. He spent a lot of time with Sanji, he was attracted to Sanji, and they had recently developed a sort of schedule for making out (which was pretty great) and so things  _ happened _ . 

The specific  _ things _ that happened tended to go as such: Sanji and Zoro are alone. Sanji is relaxing in one of his tanks. Sanji looks very nice, and Zoro wants to touch him. Permission granted, light groping begins and moves steadily into kissing. Zoro’s body gets interested in the source of his sexual desire (hint, it's Sanji) and it gets interested in a pretty obvious way. 

And at that point Zoro pulls away. 

It's not like he  _ wanted  _ to stop. It was only thanks to his iron will that he didn't jump in the damn tank with the cook, and it's not like Sanji played fair with his soft noises and hair pulling. But for all Zoro’s one half (and slightly disastrous) sexual experience went before Sanji, he had at least known the anatomy of the other guy, and therefore what to actually  _ do _ . Sanji, when in default form as his very mermaid self, was for all intensive purposes, naked. And Zoro didn't. See anything. 

Which hadn't been an issue at first, because again, default mermaid form wasn't Sanji’s only form. Zoro had clasped his hands together in thanks because if Sanji had legs, Sanji had a dick. And god fucking damn and hell did he want to get to know that dick. He wanted to be so intimatley acquainted with that dick that it responded to his fucking name. He wanted access to that dick only second to being the world’s greatest swordsman, and even then it was a close call. He was not above admitting that he had dreamed about Sanji’s dick, and even more so of his ass, because god  _ damn _ did Sanji have an ass like someone had defined the definition of perfect backside based on the man’s rear.

He was getting carried away. Anyways, Sanji had a human form, and Zoro had a mission. What got in the way of the very important mission was that Sanji, for all his stamina when it came to forms, didn't find being human to be comfortable. It wasn't  _ bad _ , but as he put it, it was like being forced to breath with his mouth rather than his nose. Kinda weird, perfectly manageable, but not preferable. And so Sanji faught, cooked, shopped, explored and performed other pirate duties with two legs, and then immediately returned to the comfort of his tanks the moment he could. Zoro came to the conclusion that Sanji probably wouldn't enjoy sex as much in his human form then, or even worse he might try and  _ bare _ it for Zoro’s sake. He decided therefore that he’d pursue intimacies with Sanji when the blue tail was present, which worked out fine since the cook instigated a good deal of the mermaid make-out sessions. Pursuing intimacies quickly hit a brick wall. Or more accurately, it hit smooth scales. 

How the fuck did mermaids have sex? Zoro hadn’t thought he'd ever be asking himself that question, and yet there he was. The simple solution would be to point blank ask, if he thought his pride could handle it. The question of whether Sanji wanted to have sex had been asnwered on a previous occiasion involving a beach party, a bit of wine, and sand stuck in all sorts of uncomfortable places. Stifled laughter, whispered encouragement, the  _ yes _ , and  _ what do you want _ and  _ how far do you want to go _ all tumbling out in shared breath until, one embarrassingly short handjob later, Zoro had been forced to hastily fix his trousers as Nami chased Luffy around their half-hidden area. Sanji fled to the water, taking away Zoro’s chance to return the favor for the time being. Still, there were more questions that would need to be asked, despite how keen Sanji always was on kissing and touching, and that one time Zoro had kissed the gills on his ribs he’d made that sound like dying-but-in-a-god-way. Exploration by hand kinda seemed rude, and the amount of things that could go wrong were downright terrifying. What if there were secret mermaid customs Zoro didn't know about? What if there was some kind of mating  _ ritual _ ? Would he have to  _ dance _ ? What if it took place underwater? How would he breathe? It was complete bullshit that all the books on mermaids were about claimed sightings and appearance and not even a little about their reproduction. Out of curiosity, Zoro had looked into the reproductive life of fish, and decided to immediately go to bed and to never try and connect what he had read to Sanji. 

He decided that he’d just have to take the risk and ask Sanji for the details. If he didn't get hit in the face with a tail for asking, then he’d move forward from there. 

-oOo-

Sanji was getting frustrated. 

For the third time that week Zoro had brought foreplay to a stop, made up some excuse and straight up ran away. It was one thing if Zoro didn't want to go further than making out, despite that time on the beach and his constant hard-ons, but it was quite frankly  _ rude _ to just run away like that. Sanji was starting to worry it was because of his appearance. He knew he looked pretty weird as a mermaid, and maybe he’d given himself too much credit in his human form too. He hadn’t paid too much attention to his overall looks other than fretting about making sure he appeared as a passable human and well groomed. He’d gotten a fair share of salacious offers and lingering looks on the Baratie, but he’d also been the only staff member who didn't look like a recent jailbird and was under 30. He’d taken up a few of said salacious offers out of curiosity more than anything else, but he’d always ended up thinking about how much more enjoyable everything would’ve been in his natural form. That, and as it turned out sex could be quite tireing and he always wanted to retire to the salt water after. He’d simply assumed for so long that he’d never get the chance to have sex as a mermaid, what with it being his secret and all. Now that he was with Zoro, and on a ship where he was safe and trusted everyone, he was pretty damn excited to try things out with his tail still present. 

Except apparently he was either horribly unattractive or Zoro was uncomfortable with mermaid sex. Sanji sighed, leaning back into his underwater couch. He stared moodily at his tail, moving it back and forth. Was it the shape? It couldn't be the color, right? Ug, it was probably his skin. All shiny like a rock or something. Maybe not though, if Zoro still liked to kiss him. Were the fins the problem? Sanji sighed again, rolling onto his stomach. It was getting late, but he didn't feel like going all the way down to the boys room and seeing Zoro’s stupid face. He pressed his face into a bright pink pillow and blew out a stream of bubbles. 

He startled when the galley door opened. He readied himself for Luffy’s attempt at a midnight snack, but was surprised to see Zoro. Sanji huffed and pushed his face back into the pillow. 

“No booze, get out.”

“I can't hear you with your face in a pillow. And underwater.”

Sanji rolled himself over with great effort. Zoro was leaning on the tank, looking down at him from over the rim with one hand dangling in the water. Sanji was tempted to smack it out, knowing it was unwashed. 

“I said, I’m not giving you any alcohol.”

“Didn't come here for that. You sleepin’ here tonight?”

Sanji looked at Zoro carefully. This seemed like normal pre-make-out behavior from the marimo, but he could also just be addressing a casual concern over his sleeping arrangements. It was Zoro after all that always checked on him or offered to carry him from tank to tank. Usopp called it mermaid duty, and Nami called it boyfriend duty. Luffy called it fish duty once, and learned quickly not to do so again. 

“Maybe. What’d you want then?”

“I was hoping for a pretty mermaid, but not if you wanna sleep.”

Ah, a flirting marimo then. Fishing for (ha, fishing) a kiss after all. Sanji was caught up in the word ‘pretty’ though. Zoro had called him pretty before, but even Luffy had called him pretty and just about anything could be ‘pretty’. Hell, even a dead crab could be seen as ‘pretty’. Sanji didn't know if he, himself, was something that qualified as nice-looking on an above-average standard. It was weird to be aware of that suddenly, out of the stressful concern for just looking human vs. looking  _ nice _ . Nami, of course, was gorgeous with her freckled skin and bright smile and brighter hair. He wasn't sure  _ why  _ she was so attractive though, she just  _ was _ . Something about face symmetry maybe? Luffy was good looking in a nice way, because his smile was so open and large. He had a tiny nose and giant eyes like a puppy, with the attention span to match. Even Usopp was nice to look at with his soft dark chocolate eyes, large like Luffy’s but with a gentler tone. Zoro’s appearance was the exact opposite, with all his sharp edges. Square jaw and high cheekbones to go with bulging muscles. Again, Sanji had no way to describe  _ why  _ he was handsome, only that he was. It wasn't like his stained shirt and bad table manners helped, but Sanji couldn't think of him as unattractive in the least. 

Sanji broke the surface to look the swordsman in the eyes. 

“Am I attractive?”

Zoro seemed to choke on nothing for a second, and Sanji waited. Zoro wheezed and thumped his chest, face red as he got his breathing back under control. 

“Uh, yeah I’d- yeah.”

Zoro seemed intent on not meeting Sanji’s eye. Annoyed, Sanji crossed his arms. 

“Ok, so are you attracted to me then?”

That made Zoro look up. He looked mildly horrified, and Sanji couldn't help his disappointment. It must have shown on his face because Zoro raised his hands and rushed to speak.

“Yes! Yes, I’m- yeah. A-attracted to you.”

Sanji didn't feel very convinced by that answer. He crossed his arms tighter over himself. 

“Do you like me better as a human?”

Zoro looked like he’d rather be anywhere else than in the current conversation. Sanji started to duck back under the water but Zoro grabbed his hand, stopping him. 

“No! I mean, I like both of- you. I like  _ you _ , y’know?”

Sanji didn't. He felt like he was talking in circles a bit, and figured he’d just go with a different direction. 

“Do you dislike sex?”

Zoro started doing the choking thing again. 

“What the fuck. No, wh-

“So why do you always run away from me when you get hard!?”

Zoro turned an impressive shade of red as his mouth fell open. Normally Sanji would have found it cute or endearing, but right now he was more focused on the answer. 

“You-

“If you don't want to have sex, fine! But if you do and the tail freaks you out or whatever-

“Holy shit, cook, it's not that.”

Sanji felt his own blush rise as Zoro took his face in his hands. He liked Zoro’s hands a lot, liked how warm they were and how rough the skin was. Now Zoro used them to gently cup his cheeks, looking him in the eyes. 

“Sanji, you’re beautiful.”

What?

“Huh?”

Zoro thought he was beautiful? That was. Well shit. He’d never been called beautiful before. Zoro really thought that?

“You’re beautiful, and handsome and gorgeous and all those things. Seriously, have you ever seen yourself? And I love your tail, it's all smooth and graceful like you.”

Mind reeling, Sanji stared at Zoro. He couldn't really think of any way to respond to that, not without freaking out a little. He went ahead and pushed all that into a neat little box in his brain and moved back to the previous topic. 

“So...why don't you want to have sex with me?”

Zoro looked like he swallowed his own tongue a few times, but then took a deep breath like he was preparing himself. Sanji watched very closely. 

“Sanji, I don't know  _ how _ .”

Out of all the things Sanji expected, that sure as fuck wasn't it. 

Didn't know how. Didn't know how? He said he wasn't a virgin before though, and- didn't know  _ how _ ? Even if it wasn't spelled out it was pretty damn obvious how to at least-

Wait. 

Sanji looked down at himself. White skin merging with blue scales, continuing down until the delicate lookings fins split. A long expanse of smoothness with no hint of a bump or opening. 

Oh. Right. 

Whoops. 

“Ah.”

Sanji felt his own blush spreading over himself, completely blindsided by the fact that yes, ok, this was indeed an issue he had never considered. It wasn't Zoro’s fault, it wasn't like he could be  _ expected _ to know how mermaid anatomy worked. Sanji had been so used to switching between species and being open about it on the Going Merry that he had all but forgotten that his experience doing that was rather unique. Zoro just had knowledge of one form of downstairs equipement, and Sanji had the two. 

“Thats- fair. 

Zoro opened his mouth, then closed it. They both chose points of the room to look at awkwardly while Sanji thought about his next options. He cleared his throat in what he hoped was a casual manner and soldiered on. It was pretty clear he was going to be leading this awkward show. 

“So, uh, I guess do you want-

“Yes.”

Sanji turned back to Zoro, raising a brow. Zoro turned the shade of a pomegranate. 

“Sorry. Uh, continue?”

“...I was gonna ask if you wanted to know how-

“Yes- shit, sorry. Fuck.”

Sanji laughed a little, the tension in his shoulders easing a bit. He leaned in to kiss Zoro, an action much appreciated judging by how eagerly he was kissed back. Sanji liked kissing Zoro quite a bit, in either of his forms. There was a new level of intimacy added now that he wasn't hiding who he was, and he doubted there’d ever be the same amount with anyone else because this was  _ Zoro _ . The boy he had known so long ago who didn't know how to swim and wanted to be his friend, grown into a man who was still gentle with him, still patient. He pulled away from the kiss slowly, smiling again as Zoro kept following his lips, chasing him almost into the tank. That gave Sanji a thought. 

“This’ll probably go smoother with you in here, marimo.”

Zoro already had one foot swung over the side of the tank before Sanji put a hand on his shoulder, stopping him. 

“If you put your disgusting boots in the water, this night is gonna end a hell of a lot sooner than we both want.”

Zoro gave his boots a betrayed kind of look, like they were personally interfering with his chances of getting laid. Sanji stifled his smile as Zoro kicked them off along with (thank god) his no doubt smelly socks. He looked at Sanji from where he was standing, waiting like a rather obedient pet for permission. Sanji was enjoying his newfound power immensely. 

“Shirt too.  _ And  _ the haramaki. I know you wipe your hands on it.”

Zoro threw off his shirt, tugging at the hideous belly warmer too, much to Sanji’s delight. When he was standing there in just his black pants, still waiting, he gave Sanji a little smirk. 

“You gonna tell me to lose the pants too, love-cook?”

Sanji pretended to contemplate that for a second. He leaned back on the farther side of the tank, schooling his face into something bored. He still couldn't quite believe Zoro was just  _ doing _ what Sanji told him to. He briefly considered making the swordsman mop the floor. What else could he get away with making him do? Questions for another time though. He wanted to get laid at some point that night, time to get things going. 

“Unless you plan on fucking me with them on…”

There was a solid second where Sanji worried he had broken Zoro, before the black pants were all but torn off. Sanji didn't even get a chance to appreciate the view (a real pity) because the mosshead was splashing into the tank with his usual lack of grace. 

“Is going commando a swordsman thi-mmmph!”

He let Zoro take control of the kiss, using the opportunity to unashamedly feel up his mossman. They didn't often have the opportunity to go at it without a barrier of glass or wood in their way, and the few times Zoro had pinned him against the counter when two pairs of legs were present, Sanji would always be forced to cut the groping session short to keep food from burning. The handjob on the beach had been a horribly rushed moment that ended in near-disaster. Now though, they were up against each other with no interruptions, and equally naked. And wow, Zoro had a  _ really  _ nice ass. Like, as far as asses went, Zoro’s was probably Sanji’s new favorite. Sanji gave it a little squeeze and yeah, definitely top of the list now. 

Sanji was just a little more interested in his other goods though. As far as dicks went, he thought Zoro had a pretty nice one. He’d seen plenty in his life, he’d grown up on a ship full of men after all. He guessed that the fact that this dick was attached to Zoro made it a particularly good dick in Sanji’s mind. It was also very hard, which Sanji appreciated. His tail was  _ not _ repulsive! Take that overly concerned brain. He reached out, letting his hand brush lightly over Zoro’s stomach, before carefully wrapping his fingers around it. Zoro gave an immediate noise of approval, still focused on licking into Sanji’s mouth. He ran his thumb along the underside, content to lazily re-explore the member for a bit as he thought about how he was going to continue. Zoro had moved one hand to Sanji’s hip, the other brushing against his gills, making the blonde gasp a little. The hand was still moving down though, carefully and slowly, but on a clear southern path. 

Sanji pulled back from the kiss with a  _ pop _ . Zoro’s hand stopped moving, and Sanji relinquished his hold on the swordsman’s decidedly nice dick. He was getting nervous again,worried about Zoro’s reaction. It wasn't like what he had was downright alien, but it also wasn't- human. It wouldn't qualify as normal, and in Sanji’s experience, what wasn't normal was usually read as weird. He gave Zoro another kiss, chaste this time, and then leaned back to look at him. 

“Ok, so, first of all, everything is behind the scales. I have to relax them, and then there'll be a, uh, an opening.”

Zoro’s mouth made a little  _ oh _ in understanding. His hand moved like it was going to go behind Sanji, and he gently grabbed the wrist, shaking his head. 

“Not like an asshole. Again, not human here.”

Zoro rolled his eyes and Sanji tugged on his ear. Zoro moved his hand back to the front, decidedly lower than it had been and without preamble. 

“Ok, so what, here?”

He pressed a little with his palm, and Sanji shuddered. Zoro stilled, eyes widening. He looked down at his own hand, Sanji’s fingers still wrapped around his wrist. 

“W-wait for me to relax the scale, you brute.”

Sanji’s voice was breathy, and even the insult came out like a partial whine. Zoro’s pupils were blown wide, and Sanji didn't have the patience to feel embarrassed. It’d been a while since he’d gotten attention like this, and he’d been pursuing Zoro for what felt like forever at this point. He was a little high-strung now, sue him. 

“Right, sorry. Just, tell me when.”

Sanji sighed, focused on relaxing. It was getting harder to think, Zoro’s length pressing against his side and the cool water warming with their bodies. He breathed in and out, and squeezed Zoro’s wrist again. He suddenly felt exposed, scales out of the way and his nakedness presented in the dim light. He jumped a little when he felt warm lips brush his cheek. 

“You ok?”

Sanji felt the tension slip away again, relief at the soft gesture filling him. 

“I never really thought anyone would see me like this. It's embarrassing I guess.”

Zoro kissed his other cheek, other hand leaving his hip to brush at the skin on his neck. 

“So it's new stuff for both of us. We’ll go at your pace and figure this out together.”

Sanji laughed quietly. It was true that they were both out of their depths (ha, depths), and it gave Sanji more of that warm feeling he got whenever Zoro did something sweet. He realized that he must trust Zoro more than just about anyone else, and that nearly knocked the breath out of him. 

“Right, ok. Ok.”

He tugged Zoro’s wrist again, bringing it up to his opening. Zoro was already reaching out, one finger just grazing the soft skin revealed under the scales. Sanji shuddered again, and squeezed Zoro's wrist in motivation. Slowly, Zoro worked a single finger into him, and Sanji let out a long sigh of absolute contentment. It felt  _ good _ , much better than his own fingers, and so much warmer. Zoro was always so warm, and so surprisingly gentle with his touch. Zoro, thankfully, wasn't just letting his finger sit there. He moved it gently, stroking the sides, feeling around. Sanji had closed his eyes, letting out more soft sighs. 

“Can I add another?”

Sanji nodded, not bothering to speak. He removed his fingers from Zoro’s wrist, using both his hands to touch the skin around the dark chest, shoulders, collarbone. When the second finger entered him, he let out a little  _ ah _ . He could almost smell his own arousal in the air now, felt the wetness in him easing Zoro’s movements. If the other man noticed this, he was only taking it as encouragment, moving his fingers back and forth, slowly fucking him. It felt so good, and Sanji just wanted to let him do it forever. 

Zoro crooked his fingers, moving a little deeper than before and Sanji let out a low moan. Zoro’s cock twitched at Sanji’s side, interest peaked. Without needing to be told to, Zoro repeated the action, and Sanji rewarded him with the thrust of his own hips. The drag of the cock on his smooth scales was somehow gratifying, and now Zoro had found the spot to aim for within Sanji. He was abusing it, pressing into it light and quick, and Sanji was starting to see stars. 

“Ah,  _ ah _ , more, add- add another.”

Zoro was panting in his ear, leaning his full body against Sanji’s now. He had three fingers in Sanji, and it was almost perfect. The heat, his chest pressing on Sanjis, the water sliding off them both, it was all so good. Zoro seemed to have gained confidence, moving his fingers this way and that, making Sanji cry out in a way he would be embarrassed about later. He was losing all pretense of being composed, breath coming out in pants or moans, and all he could do was hold onto Zoro’s shoulders now. At a hard thrust of fingers, Sanji released his own hands and fumbled down for Zoro’s cock, pumping it firmly. Zoro groaned in his ear, movement stuttering. 

“Sanji-

“In me, c’mon, please, I need you  _ in me _ .”

Zoro gave another ragged moan in his ear, body shuddering. Sanji was practically dragging his cock to his hole, desperate. If Zoro didn't get inside him  _ right now _ he was going to  _ die _ . He felt the press of Zoro entering him, the slide as he pushed in an  _ god, fuck, yes yes yes yes- _

Sanji’s tail had wrapped around one of Zoro’s thighs, pulling him in more, helping him to fuck Sanji faster. It was perfect, it was  _ so fucking perfect _ , god the heat, he could practically feel Zoro pulse in him, feel ever vein as he settled inside like he was made to be there. Sanji kissed blindly, finding the side of a mouth, a cheek, a sweat-slick neck. 

“You feel so good in me, so fucking good, Zoro.”

Zoro made a noise like he was dying, pushing his face into Sanji’s neck to bite at the skin there. He licked it, tongue rough on the pale expanse. Sanji tried moving his hips a little, but Zoro’s hands came down, clamping over his hip bones like a vice, fingers trembling as they kept Sanji still. 

“Wait, wait, too good, I’ll come. Fucking-

Sanji bit his lip hard to keep from laughing. It seemed he wasn't the only one heavily affected, if anything he was apparently the  _ less _ affected. Zoro was trying to take steady, controlled breaths, fingers flexing against Sanji’s skin. 

“Wow, arent swordsmen supposed to have good stamina?”

“Fuck you, just gimme a second.”

“I am, in fact, waiting to be fucked by you, so.”

Zoro growled into the skin on his neck, and Sanji felt a cruel smirk creep along his face as he flexed and squeezed around Zoro’s member. Zoro gasped, hands pressing into Sanji’s skin so hard he’d probably leave bruises. Sanji liked that thought. 

“ _ Sanji _ , please, d-don't wanna come, not yet.”

Sanji felt himself release more slick, getting hot all over. Oh god did he want Zoro to come in him, feel him release and throb- but not yet. Zoro was right, as hilarious as his lack of control right now was, Sanji wanted to be fucked  _ so bad _ . 

“Ok, I’ll be nice. Poor staminaless marimo.” 

Zoro licked along the shell of his ear, and Sanji shivered at his hot breath. 

“I’m gonna find a way to make you shut up, just you fucking wait.”

“Big words coming fr-  _ oh FUCK _ !”

Sanji didn't have time to roll with the thrust, just taking it as it hit him right on the tight bundle of nerves deep inside him. It felt unbelievable, like everytime Zoro touched it he was lighting Sanji on fire and in the next second plunging him in ice water. It was a pleasure that bordered right on too-intense, and Sanji didn't want it to ever stop. He wrapped his arms around Zoro’s neck, pressing himself as close as he physically could. Zoro’s hips pistoned in and out, cock sliding easily as slick dripped out of Sanji’s hole. Water sloshed over the side of tank as Zoro’s thrusts became more erratic. Sanji heard himself making little noises against Zoro’s neck, heard the way that Zoro’s name kept slipping off his tongue. 

He wasn't going to last. He’d given Zoro shit earlier, but he wasn't any less desperate after the waiting game they’d played. Everything just felt  _ right _ in a way it never had, being in the water and breathing so easily with Zoro’s arms holding him steady. He wanted to get even closer to Zoro somehow, push his chest into his until the skin melted away and maybe then even closer. He moved out of the safety of Zoro’s neck, kissing him hard on his open mouth. Zoro moaned against his lips, and Sanji wanted to scream with how close he was. 

And then their heads were below the surface of the water, with Zoro taking in the air Sanji gave him and fucking him hard and sweet all at once. If there was an intimacy beyond this he couldn't think of it, and he came with a silent scream. His entire body tensed, tail probably crushing Zoro’s leg, and he felt the other man come in him like sparks on his skin. 

  
  


-oOo-

  
  


Zoro didn't know how long they stayed there before he pulled them back up, breaking the surface. His chest hurt, like he couldn't get enough air if he tried, and he could feel bruises on his neck blooming. He wiggled his left leg, briefly wondering if Sanji had fractured a bone there. If so, worth it. 

Sanji was panting on his collarbone, wet hair falling on his face in that soft way it never did with humans. Zoro pulled out gently, grimacing at the feeling of saltwater and cum swirling around him. Sanji gave a sigh, eyes still closed. He wore a blush all the way down to his chest, rosy hue mingling with the start of purple at his hips. Unless he wore a shirt in the tank tomorrow it would be pretty obvious what he’d been up to. Zoro figured everyone already thought they were banging anyways. 

He kissed the top of Sanji’s head, hand coming up to brush some of the hair away. His blue eyes cracked open, looking up at him lazily. 

“You ok?”

Sanji blinked at him, brain still foggy. He nodded, a slow smile starting on his face. He started to chuckle quietly.

“We just had mermaid sex.”

Zoro let out a snort or laughter, which grew into a full bellied laugh. They  _ had _ just had mermaid sex. He and Sanji were officially mermaid virgins no more. Who’d have thought he’d be so happy about such a niche area of sex, or that it’d involve him at all in his lifetime. 

“Y’know, I think it beats regular human sex.”

Sanji raised a brow at him, face still pressed against his skin. 

“Really? I get it being better for me, but you had to get in a water tank and deal with strange anatomy.” 

Zoro laughed again, fingers reaching down to tickle Sanji’s gills. He jumped, tail almost whacking Zoro in the dick. For his part, Zoro was pretty confident that the quality of the sex had a lot to do with the fact that it was with Sanji, and in whatever form he took it would be good.

“Not really that different from any of the human bits. Plus the water has its appeal.”

He was already thinking of a few creative ways to throw around Sanji’s weight. Would it be weird if he wore a snorkel durring sex? Eh, he’d figure it out. He yawned, suddenly exhausted. Sanji leaned over the side of the tank, nudging Zoro. 

“C’mon, I’m not sleeping in your cum water.”

“You came in it too.”

“Get your ass out of the tank, marimo.”

Zoro lifted himself over the side of the tank, grabbing his clothes. It was a bitch getting his pants on while he was still wet, and the shirt was mostly damp. He left his shoes wherever they were and walked back over to the tank. Sanji was watching him, hair messy and tired looking. 

“Want me to carry you like a princess?”

“Fuck you. Yes.”

Zoro did. He’d done this pretty often anyways, being the only one besides Luffy that could actually hold Sanji’s weight, and because he liked carrying him. Sanji’s arms came up automatically to wrap around his neck, wet skin cool against Zoro’s overheated flesh. He was so beautiful, Zoro thought. He had a small smile on his tired face, long fingers touching the back of Zoro’s neck as he was being held, and Zoro had to kiss him again, caught in the view of something that beautiful. He hoped that he could press his love for Sanji into that kiss because he was awful at saying it out loud, didn't even know how to really, but when they were this close and Sanji smiled into the kiss, he nearly prayed that Sanji understood. The kiss broke gently and the air was cold on their wet skin, reminding Zoro that sex and romance and love didn't mean they were immune from real life. 

When they got down to the boys room, it was quiet, save for soft snoring by Luffy and Usopp. Zoro placed Sanji in his sleeping tank carefully, the netting lining the bottom acting like an underwater hammock to sleep in. Sanji immediately curled up in the mesh, sunken pillow lightly bouncing in response to his movement. Zoro flopped back heavily into his own hammock, feeling like he could pass out any second. His skin prickled uncomfortably though, making it hard to relax.

He stared at a spot on the wall for what felt like a couple minutes, feeling restless for no good reason. There was too much space around him, and the air was dry and too warm. His hand twitched, and he rolled over onto his side to look at Sanji.

He was looking back, large blue eyes blinking slow and sleepy but with the same hint of restlessness that Zoro felt. Sanji pressed his palm against the glass, and Zoro reached out to meet it. Sanji stared at their hands silently, tail flicking. The water seemed to glow in the dark, making ripples dance over Sanji’s skin. Zoro rolled his legs over the side of the hammock, tugging his damp shirt over his head. In the next second he was stepping into the tank, pants clinging to his skin uncomfortably. Sanji looked like he wasn't sure what was happening. 

“Can I sleep in here?”

Sanji blinked at him, and Zoro watched the bright pink spread over his face. He gave a sharp nod, head lowered to try and hide an obvious smile. Zoro grinned, holding the sides of the tank as he lowered himself down, Sanji’s arms already starting to wrap around his torso. He brought his head up, fitting it against Zoro’s collarbone in a way that would keep Zoro from drowning in his sleep. 

It wasn't comfortable. The water was a little cold, the tank walls were hard on his back, but he didn't have it in him to care. Sanji gave a soft little sigh and he wrapped his arms tighter around him, holding him close. 

He was asleep within seconds. 

  
  


-oOo-

  
  


Nami opened the trap door to take a quick peak, not at all surprised by the sight of the two men cramped in the tank. She shook her head in amusement before silently lowering the door back down. 

She’d been on watch that night, and if Sanji and Zoro thought they’d been  _ quiet _ they were a lot denser than she thought. She wasn't about to deny the fact that she was happy for them though, and lord knew Zoro would probably be a lot less grumpy now that he knew how to have sex with his boyfriend. That being said, they now owed her a considerable amount of money for all the information she did  _ not  _ want. 

She’d give them a hopeless-idiots-in-love discount though. She wasn't  _ heartless _ . 

  
  
  
  


**Author's Note:**

> wow im gonna go lie down for a week


End file.
